A plumber earns $15 per hour more than her apprentice. For a 40-hour week, their combined earnings are $2200. What is the hourly rate for each person?

Say the apprentice earns x dollars an hour, and the plumber earns x+15 dollars per hour. Write the equation:

40 (x+x+15) = 2200

Dividing by 40, we see that:

2x+15=55

Subtracting 15, we see that 2x=40, so x=20. As a result, the apprentice earns $20 an hour, and the plumber earns #35 per hour.